Electromagnetic high energy forming

ABSTRACT

Disclosed is an apparatus utilizing the forces exerted upon a conducting surface of a tool by a pulsed intense magnetic field to propel the tool against a workpiece. The conductor surface is initially positioned in a pulsed high flux density magnetic field. As the conductor is subjected to the suddenly rising magnetic field, electrical currents (so-called eddy currents) are produced by the passage of the field into the conductor surface developing an intense force repelling the tool away from the means generating the magnetic field. The working surface of the propelled tool imposes a high density force against the workpiece suitable for cutting or otherwise forming it. A specific application of such a tool for installing rivets is described in detail. The improved riveted structure produced by the electromagnetically propelled riveter is also disclosed.

United States Patent Orr et al.

. Dec. 5, 1972 ELECTROMAGNETIC HIGH ENERGY FORMING Inventors: La Vern G.Orr, Auburn; Nobuo Yutani, Seattle, both of Wash.

Assignee: The Boeing Company, Seattle,

Wash.

Filed: Aug. 1, 1968 Appl. N0.: 749,386

US. Cl. ..29/243.54, 29/421 M, 72/430, 72/56, 317/151 Int. Cl. .....B23p11/00, B2lj 15/24, B2ld 26/02 Field of Search...72/56, 430; 29/421 M,243.53, 29/243.54, 254; 317/151; 307/116; 83/575 References Cited UNITEDSTATES PATENTS 6/1948 Fischer ..72/407 X 3/1965 Diebold ..29/421 M UX7/1969 Wildi ..310/27 12/1966 Gerber et a1. ..83/575 PrimaryExaminer-Andrew R. Juhasz Assistant Examiner-Leon GildenAttorney-Christensen and Sanborn [57] ABSTRACT tool away from the meansgenerating the magnetic field. The working surface of the propelled toolimposes a high density force against the workpiece suitable for cuttingor otherwise forming it. A specific application of such a tool forinstalling rivets is described in detail. The improved riveted structureproduced by the electromagnetically propelled riveter is also disclosed.

31 Claims, 6 Drawing Figures .rlillii BANK PATENTEDHEB 5 I912 SHEEI 2 0F2 W LWW ATTORNEY? ELECTROMAGNETIC HIGH ENERGY FORMING BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to apparatusfor mechanically forming material and relates more particularly toelectromagnetic apparatus which strikes the material with a high densityforce such as required to install rivets with a single impact.

2. Description of the Prior Art Several techniques have been developedover the course of recent years for mechanically forming materials. Insome techniques electrical energy is converted into a mechanical forcewhich is used for blanking, shearing, forging, anchor setting, pressurewelding, stamping, dimpling, hammering, punching, chipping, indenting,deforming and other similar operations in order that the materialsubjected to such an operation may be made more useful. In the patent toMichlein, U.S. Pat. No. 2,752,061, a mechanical force is used to causecold plastic flow of the tubular portion of a rivet to properly installthe rivet in place. As disclosed a solenoid is used to directly supplythe power required in the production of the work stroke.

In the patent to Birdsall et al., U.S. Pat. No. 3,088,200, an electricalconductor material in tube form is mechanically forced into the shape ofan internal mandrel due to the pressure of a magneticfield imposed uponthe conductor material as a result of a suddenly rising magnetic fielddeveloped in a coil wrapped around the tube.

In the patent to Falcioni, US. Pat. No. 3,292,413, an aircraft rivet isinstalled by mechanical forces developed by an opposed pair oftransducers vibrating at a frequency in excess of 20,000 cycles persecond with the transducers placed in contact with opposite ends of therivet.

In the patent to Golden et al., US. Pat. No. 3,345,843, the material isforced into a new die configured form as a result of the energy of ashock wave striking the material originally propagated by the suddendischarge of electric energy across an electrode gap in a liquidcontaining the material.

In each of these techniques electrical energy is transformed into amechanical force useful in forming the workpiece involved. Each of thesetechniques, however, have certain inherent features which limit theirusefulness. In the magnetic shaping process of Birdsall; et al., and inthe electrohydraulic shaping process of Golden, et al., the workingforces applied against the workpiece are more or less uniform andtherefore not concentrated at any particular focus point against theworkpiece. The ultrasonic vibrating forces of the Falcioni apparatus maybe useful for installing rivets of relatively soft materials but thework hardening which results from repeated impacts on certain hardermaterials such as titanium often cause the rivets to crack and losetheir strength.

While the solenoid rivet setting tool of the Michlein apparatus doesserve the purpose of focusing the impacting force of the tool againstthe workpiece, the maximum force developed by a solenoid type device islimited by the saturation effects in its ferromagnetic material and isat most several hundred pounds. For example, in column three, line twoof this patent, the force applied to install a small rivet was found tobe in excess of 1,600 pounds. Even if the cross section of a solenoidplunger were as small as 0.0001 square meters, the maximum forcedeveloped by such a plunger is about 1,800 pounds because of saturation.

While it is general practice to use a coil of conductive material togenerate a magnetic field, the heat generated and the mechanicalstresses induced in the coil by the pulse of electrical energy throughthe coil generally reduce the useful life or rate of operation of suchcoils. Production speeds of equipment using such coils are often limitedby such useful life considerations.

It is therefore seen that previous techniques for converting electricalenergy to a mechanical force for forming materials do not provide aneffective system for focusing mechanical forces of sufficient magnitudeagainst a selected portion of the workpiece in a short time. Inaddition, massive frameworks have been considered necessary beforeequipment would be thought suitable for a system for imposing andreacting from the magnitude of force necessary to install rivets havinga three-eighths inch diameter or made of high strength material such astitanium. The squeeze type riveting machines capable of meeting the highinstallation force requirements anticipated for the supersonic transportare massive to the point of being larger than a house and very costly tothe extent of several hundreds of thousands of dollars per machine.

Although it has been proposed that rivets be installed by one hammerhitting on one end of the rivet while another hammer is hitting on theother end of the rivet, the driving mechanism for such hammers have notproduced the desired synchronous action. Use of mechanical, pneumatic,hydraulic, electrical or combination of these methods fail to providesynchronous action and in fact produce inconsistent and unreliableresults because of system inertia or compressability effects.

In the field of riveting aircraft structures several problems areconfronting the riveting equipment designer. Not only are thesestructures becoming larger and thereby requiring longer and largerrivets but also such structures are subjected to increased utilizationrequiring rivet installations of increased strength and sufficientfatigue life to ensure a profitable return on the purchasers investment.Such joining of structures also require more force to install.

SUMMARY OF THE INVENTION AND OBJECTS From the foregoing discussion ofprior art techniques for material forming, it is clear that there is aneed for a simply constructed, easily used apparatus for applying a highdensity mechanical force. It is therefore the principal object of thisinvention to provide a generally improved apparatus for convertingelectrical energy into a mechanical force of high density useful informing materials.

It is another object of the instant invention to provide a materialforming apparatus which is capable of exact control for repeatable workforce outputs.

It is a further object of the instant invention to provide a high energydensity material forming apparatus capable of producing a sufficientforce in one blow against a workpiece to thereby avoid the degradationin the workpiece properties resulting from repeated blows necessary inother systems to provide the same degree of forming results.

A still further object of the instant invention is to provide anapparatus for forming materials which applies the high energy force in atime measured by microseconds while at the same time includes a systemfor synchronizing the application of force by two or more such apparatuswith great precision.

It is a related object of the instant invention to provide an improvedcoil structure useful in an apparatus for converting electrical energyto high density mechanical force including the provision of means forextending the useful life of the coil by minimizing the degradation dueto system heat generation and by the provision of mechanicalreinforcement for the coil.

A still further object of the instant invention is to provide animproved force application tool which is useful in applying a highdensity mechanical force to properly form a workpiece such as a rivet.

It is an additional object of the instant invention to providestructures which are joined by rivet installations having excellentstrength and fatigue life.

It is also an object of the instant invention to provide a rivetingapparatus which in addition to providing high density forces for rivetinstallations, also provides independent systems for part clamping andrivet-to-die preloading.

A still further object of the instant invention is to provide agenerally improved riveting apparatus which because of it ability toapply such a high density rivet setting force in such a short time doesnot require a massive framework to ensure precise alignment of the tool.

Another object of the instant invention is to provide a recoil mechanismsuitable for use in a high energy impact tool.

In accordance with the present invention, electrical energy is convertedinto a material forming mechanical force. The electrical energy isaccumulated to provide hundreds and thousands of Joules at severalthousand volts in a storage system such as a capacitor bank.Periodically through a discharging circuit an electrical current ispassed through a flat wound coil to develop a rapidly rising, highdensity, magnetic field adjacent to the coil. The transducer or toolportion of the apparatus includes an electrical conductor surface placedadjacent to the flat wound coil within its magnetic field. Through thebody of the tool a work application surface is connected to theconductor surface. As the electrical energy is discharged through thecoil the rapidly rising magnetic field causes eddy currents to developin the conductor surface producing a high energy repelling force betweenthe coil and the conductor surface which propels the tool and its forceapplication surface against the workpiece. If a double hammer system isused, exact synchronization between the propelled work applicationsurfaces against the workpiece is possible through the use of a seriesconnection between the two coils driving the two tools. The temperatureof the coil can be controlled by injecting cool air or other suitablefluid against the surface of the coil and conductor plate. Since theimpact of the tool against the workpiece is of a very short duration, itmay be reacted by a suitable suspended mass recoil system, rather thanas a static force through, a massive riveter frame. For installingrivets, heading die shapes are used which restrict the expansion of theformed headyielding uniform radial expansion of the rivet and excellentjoint strength and fatigue life.

These and other features and advantages of the invention will becomemore clearly apparent from the following detailed description thereof,which is to be read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a diagrammatic view of the generalized embodiment of theinvention with portions shown in crosssection for clarity;

FIG. 2 is a side elevation view illustrating an opposed hammer rivetingembodiment of the instant invention;

FIG. 3 is an end elevation view of a portion of the opposed hammerembodiment of the invention with portions shown cut away or in sectionfor clarity;

FIG. 4 is a section view of the invention as seen through lines 4-4 ofFIG. 3;

FIG. 5 is a partial side section view in enlarged scale illustrating arivet just prior to installation; and

FIG. 6 is a partial side section view showing the rivet of FIG. 5 as itis completely installed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

With reference to FIG. 1 it is seen that the general embodiment 5 of theapparatus of the instant invention includes within its system anelectrical energy source 10 to provide the necessary electric currentfor the magnetic field generator 15 for driving the transducer 25 withthe resulting mechanical force applied in a first direction 48 againstthe workpiece 50. The electrical energy source 10 may include anysuitable system for providing a high pulse of electrical current and, asshown, this is provided by capacitor bank 11 and a high current switch12 connected in series with the magnetic field generator in the form offiat wound coil 17. Of course other cross-sectional shapes can be usedfor coil 17. As shown, coil 17 is'formed by coiling a fiat conductorribbon such as copper to produce a number of turns having an outsideterminal 18 and an inside terminal 19 at opposite ends of coil 17 forconnection with energy source 10. Insulating material 21 is interspersedbetween the individual turns of the coil 17. One face 20 and the outsidesurface of coil 17 are supported by insulating casing 22 and the otherface 23 of coil 17 is supported by a membrane 24 made of wovenfiberglass or other similar strong insulating material.

When coil 17 is subjected to a high discharge of current from electricalenergy source 10, there is a tendency for it to straighten out. Thistendency is resisted by casing 22. The current also tends to cause coil17 to unwind or spring in its axial direction. This movement is resistedby membrane 24 for the motion in a first direction 48 and by casing 22for motion in the opposite direction. By utilizing a flat material forcoil 17 in contrast to a circular conductor material, there is a greaterfrictional surface area presented along the first direction 48 forresisting the tendency for the coil to spring outwardly along itscentral axis. Insulation material 21 in the form of a potting compoundsuch as adiprene or an epoxy system can be used along with fiberglasstape or conventional transformer paper to insulate one turn of the coilfrom another.

Transducer 25 may be composed of any single or combination of forceresponsive and transmitting materials with sufficient rigidity and formto support a sheet of conducting material such as copper plate 27 at oneend of body 28 of transducer 25, with the surface of the sheet 27generally parallel to face23 of coil 17 adjacent to membrane 24. In onesuch apparatus the surface of sheet 27 is initially 0.06 inches awayfrom face 23 of coil 17. At the other end of transducer body 28, in thefirst direction 48 from the conductor sheet 27, is positioned forceapplication tool 30 which may be attached to body 28 by means of threads3l.'As shown, tool 30 is shaped as a chisel useful in cutting off thehead of bolt 52 or otherwise forming workpiece 50. Clamp 54 holdsworkpiece 50 and the whole assembly is supported by frame 40 whichincludes back stop member 42 in contact with the coil casing22 and guidesupports 44 having bearings 45 in guiding contact with transducer body28.

In operation, general embodiment 5 is initially positioned as shown inFIG. 1. When a working stroke is desired, high current switch 12 isclosed permitting electrical energy from capacitor bank 11 to bedischarged through coil 17. This high energy pulse of electrical currentpassing through coil 17 develops a rising magnetic field adjacent tocoil 17. Since conductor sheet 27 of transducer 25 is positioned withinthe effective magnetic field developed by coil 17, a current is producedin sheet 27 that is proportional to the field intensity at its surface.The interaction of the field and such induced current produces arepelling pressure or force between coil 17 and transducer 25. Thisinstantaneous and tremendously intense repelling force between coil 17and conductor sheet 27 imparts motion to transducer 25 along firstdirection 48. This propelling force is of such high energy that tool 30easily severs bolt head 52 away from its supporting workpiece 50.

Although electrical energy source may be charged to several thousandvolts, the amount of power involved is not unreasonable since apparatus5 may be tired every 10 seconds with normal household current andvoltage feeding the electrical source to charge capacitor bank 11between individual firings. This result is obtained because of the veryshort cycle time, as measured in microseconds, for the actual dischargeof the energy through coil 17.

By varying the form of the force application tool, it is possible to usethe above described apparatus for a great number of material formingoperations. Holes may be punched, dimples may be formed, edges may becut, patterns may be imprinted, objects may be hammered, and sheets maybe shaped, parts may be forged, anchors may be set, plates may bepressure welded, with all of these operation utilizing the extremelyshort pulse high density force provided by the apparatus of the instantinvention.

For a better understanding of the basic principle and particularadaptability of such apparatus, a detailed description of itsutilization in the forming of rivets is presented.

At the present time there are tremendous demands placed upon thedevelopers of riveting equipment to meet the needs of the aircraftindustry to rivet structures which must withstand higher loads andgreater ranges of temperature. Greater service life is demanded ofcommercial airframes to provide a sound structure with greater fatiguelife. Larger structures are being developed which require thicker sheetsof material to be joined by riveting. This situation results in therequirement for both longer and larger diameter rivets of strongermaterials which ultimately require a greater force to install andmustprovide greater reliability in any single installation. Whilereferring to rivets herein we include all forms thereof since theapparatus inv volved is not materially different regardless of whetherthe rivet is in the form of a simple cylinder, a tapered plug, acylinder with a manufactured head or of another configuration.

If the present trend of the state of the art in riveting equipment isfollowed, massive frameworks requiring railroad track support structureswill be needed to produce the squeezing force necessary to install alarge rivet made of titanium or other similar high strength material. Itis clear, however, that the high initial cost in the form of a highcapital investment forsuch equip ment adds significantly to the cost ofproducing the products utilizing such rivets. It has been found that theuse of repeated impacts of a lower force to form the rivet of somematerials is unacceptable since such rivets become work hardened andhave a tendency to crack due to the repeated impacts of the hammeringsystem. In installations requiring fuel tight riveting and good fatiguelife, repeated impact riveting is often unacceptable because therepeatability of net energy imparted to the rivet is difficult to obtainsince the dynamic response of the workpiece affects the energy contentper impact. In addition, the noise generated by the hammering type ofriveting equipment adds materially to thefatigue of the employeesinvolved inthe riveting area.

To make more clear the significant forces involved in forming the largerstronger metal rivets, it is appropriate to start with a comparisonbetween the 1,600 pounds required to form a rivet having a diameter of0.140 inches as disclosed in the previously mentioned patent toMichlein, with the 32,000 pounds equivalent static force required forforming a stainless steel rivet of 0.250 inches in diameter.

To accomplish the previously related demanding rivet installationfunction the opposed synchronous rivet hammer apparatus 60 shown inFIGS. 2 to 4 has been developed. With reference to FIG. 2, it is notedthat opposed hammer riveter 60 is supported by a C shaped frame 65mounted on pedestal legs 68 and 69 which are supported by the floor 70.A convenient eyebolt 72 may be used with a suitable crane to moveriveter assembly 60 from one work station to another within themanufacturing plant so that riveter 60 is readily adaptable to performriveting on panels positioned in place in assembly tools or jigs.Support pads 75 and 76 are mounted on the open ends of the C frame 65 toprovide alignment of the upper and lower rivet hammer units 79, 80 alongthe rivet axis 83.

With continued reference to FIG. 2, it is noted that sheets and 86 canbe clamped within frame 65 through the application of clamping pressurefrom upper and lower clamping fluid motors 89 and 90.

These motors are attached to the pads 7-5 and 76 through support plates93 and 94. Connecting rods 97, 98 project out from the motors 89 and 90against the cap members 101, 102 of the hammer units 79 and 80. Clampingpads 105 and 106 actually engage the surfaces of sheets 85 and 86 andare spaced from cap members 101 and 102 by spacing rods 109 and 110slidably supported within support guides 111 and 112 anchored to supportpads 75 and 76. As pressurized fluid is supplied to clamping motors 89and 90 in a conventional manner, clamping, pressure is placed uponsheets 85 and 86.

Hammer units 79, 80 will be described in more detail with reference toFIGS. 3 and 4 but it should be noted the upper hammer coil housing 115defines two iongitudinal conduit slots 117 and 119 providing electricalconnection to the hammer coil 163 by terminalconnectors 129 and 139.Similarly lower coil housing 116 defines conduit slots 118 and 120 forterminal connectors 130 and 142. If required for coil temperaturecontrol, cooling. medium can be applied to the coils through conduits123 and 124 which may project through the slots 117, 119 and 118, 120.If desired each coil may be designed to permit the cooling medium to runthrough the body of the coil itself.

The electrical energy supply system 125 for opposed hammer units 79 and80 is shown in FIG. 2 with the first point of interest being the use ofa series connector 127 extending between terminal connector 129 of upperhammer unit 79 and corresponding terminal connector 130 of lower hammerunit- 80. Capacitor bank 132 and the high current switch, shown asignitrons 133', are connected in series through lead 134. lgnitrons 133are connected through lead 137 to terminal connector 139 of upper hammerunit 79 and capacitor bank 132 is connected through lead 140 to theother terminal connector 142 of lower hammer unit 80. To provide thesequencing and timing function useful in controlling the amount ofcharge and the time of firing the charge through the hammer unit coils,suitable controls 144, firing circuit 145 and power supply unit 147 areconnected to ignitrons 133 and capacitor bank 132, as shown in FIG. 2.

As shown in FIG. 3, rivet 87 extends along rivet axis 83 and projectsthrough sheets 85 and 86. In line with rivet axis 83 and defined withinclamp pad 105 is a tool channel 149 extending through the pad member105. Positioned within and slidable along channel 149 is the heading dieor working surface 151 of the transducer 153. An electrical conductorsurface plate 155 is secured to transducer 153 in a firing position inintimate contact with the membrane member 159 which seals off the lowerface or transducer face 161 of the flat wound coil 163. Positioned onthe upper side and in nonconducting contact with flat wound coil 163adjacent its recoil face 162 is recoil mass 167.

Surface 169, at the upper extreme end of recoil mass 167, serves todefine, along with the inner side walls of housing 115 and the lowersurface 171 of cap member 101, preload chamber 175. A suitable source ofgas or fluid under pressure (not shown) is supplied to preload chamber175 to, initially insure intimate contact between membrane member 159and conductor plate 155 and between working surface 151 and rivet 87. Inthe case of the lower hammer unit 80, the force of gravity pulls therecoil mass, coil and transducer downwardly away from contact with rivet87, therefore, .a similar pressurized preload chamber (not shown) isutilized to impose an upwardly directed force to prelaod rivet 87 asdesired. in addition, an adjustable preset relief valve system (notshown) may be used in preload chamber 175 to permit the escape of thesuspension gas or fluid during the recoil period when the recoil mass167 is propelled toward the cap member 101, thereby reducing the size ofpreload chamber 175 and increasing the pressure on the suspension gas orfluid. To provide easy, non-wearing sliding of recoil mass 167, coil163, and transducer 153 along the inside surface of housing 115, acoating of low friction insulating material 179, such as nylon orpolytetrafluoroethylene, is used to coat the inside surface of housing115. For safety and strength reasons, housing is made of afiberglass-epoxy laminate.

As shown in FIG. 4, coil 163 includes at one end interior terminalconnector 129. Coil 163 is wrapped around a number of turns until itreaches its other end connected to terminal connector 139. Between eachturn of the flat wound coil 163, insulating material 181 is packed inthe form of a potting compound. Precoated electrical conductor material,such as varnish or insulating paper a few mils thick, individually or incombination with a potting compound, con comprise the insulation betweenturns of coil 163.

In the course of developing a suitable flat wound coil 163, varioustypes of coil material separators and different numbers of turns wereused. For example, onesixteenth inch thick copper material has been usedfor the coils having a width of seven-sixteenths inch, with each coilseparated from one another by a layer of transformer paper and a pottingcompound of an epoxy material. Initially a coil of 12 turns with a 3inch outside diameter was used to drive a transducer having a 3 inchdiameter conductor surface. Other coils having eighteen turns with-a 5inch outside diameter were used to drive a transducer having a 5 inchdiameter conductor surface. As a number of turns increased the availableforce for propelling transducer 153 increased until at a certain pointnear forty turns the amount of discharge voltage required for the samedeformation of the rivet began to increase. This'occurred due to theinteraction of the increased system inductance caused by the increasednumber of turns of the coil and with this the increase in duration ofcurrent pulse while its peak magnitude was reduced. It was also foundthat the propulsion force due to the rising field in between coil 163and transducer 153 decreased as transducer 153 moves away from coil 163.For this reason a certain balance was obtained by noting the amount ofvoltage required for similar deformation of similar rivets with avariation in the number of turns in the coils used. A mere change of theconductor material for the conducting surface plate from aluminum tocopper decreased the system inductance of one system by 5 to 10 percent,thereby adding to the overall efficiency of this system without adecrease in the number of turns of the coil. The coil life wassubstantially increased by making more uniform the gap between adjacentcoils, opening up the interior diameter of the coil and by usingimproved potting material 181.

Recent published statements concerning the advantages of reducing theconductor width for a flat wound coil indicated that there should be anincrease power requirement of over fifty percent for doubling the widthof the coil. In a comparison test, however, it was found that two pairsof coils, being the same in all respects except that one of the coilswas reduced from inch width to Arinch width, could each suitably install0.250 inch diameter stainless steel rivets. It was noted that for thesame rivet deformation, the coils with the Vs inch width wire required4,060 Joules energy while those having a three quarter inch width wirerequired 4,500 Joules of energy. This is a power increase of only 11percent for a 6 to 1 width increase ratio as compared to the notedpublished data, which was apparently based on calculations rather thanactual observed testing. The importance of the wider strip of conductor,i.e., a conductor with a width to thickness ratio greater than 1 to l,for the coil material is that it produces a significantly increaseduseful life for the coil by having a greater surface area for resistingthe tendency of the coil to move along its central axis in response tothe tremendous surge of electrical current through the coil.

Coil life has been also substantially increased by controlling thetemperature of the coil through the use of a cooling gas such as CO ornormal plant air. Adequate cooling is obtained by directing a stream ofsuch cooling medium through conduits 123 and 124 shown in FIG. 2 towardthe region between membrane 159 and conducting surface 155 during theperiod that the coil system is recoiling after the electrical current isdischarged through coil 163.

In operation, opposed hammer riveter 60 is used to install rivet 87after rivet 87 is placed in the rivet hole formed in sheets 85 and 86.Through the action of clamping motors 89 and 90, clamping pads 105 and106 impose a clamping pressure on sheets 85 and 86 holding themtogether. A preloading of the rivet 87 is provided by increasing thepressure of a fluid or gas in preload chamber 175 causing heading die151 to press against rivet 87 and a corresponding pressure is appliedfrom the opposite lower hammering unit 80. While clamping and preloadingare not absolutely necessary for the proper operation of the unit, goodresults have been obtained by imposing a clamping pressure on the sheets85, 86 from zero to one thousand pound pounds and applying preloadpressures on the riveter from zero to five hundred pounds.

Once the equipment is in this ready to fire condition, controls 144permit the capacitor bank 132 to be discharged through the actuation offiring circuit 145 to operate ignitrons 133 so that the coils of hammerunits 79 and 80 will simultaneously receive a high energy electricalcurrent discharge. Such a discharge develops a rising magnetic fieldaround the coil 163 and particularly in the vicinity of the conductorplate 155. Since plate 155 is made of an electrical conductor, eddycurrents are rapidly developed within the rising magnetic fielddeveloping a force repelling the magnetic force of coil 163. Thisrepelling force causes transducer 153 to be propelled toward the rivet87 and this force is transmitted through heading die 151 causing thedeformation and therefore the installation of rivet 87 within sheets 85and 86. An exactly opposite and simultaneous action occurs in the lowerhammer unit due to the series connection between the coils of the hammerunit 79 and 80 provided by series connector 127. Thus there is nomechanical lag or system inertia which in any way causes a lack ofsynchronization between the opposed hammer blows applied with greatforce density against rivet 87.

Because of the repulsion between transducer 153 and the coil 163, thereis a recoil force applied to coil 163 causing coil 163 and recoil mass167 to move upwardly in an opposite direction from the movement oftransducer 153. Although the coil 163 could be held rigid as inembodiment 5 of FIG. 1, the free suspension of coil 163 in housing 115with a backup recoil mass 167 permits the use of a light frame forriveter 60. A weight ratio between mass 167 and transducer 153 of over10 to 1 will provide some propulsion useful for moving transducer 153against rivet 87 with a better energy efficiency resulting at a weightratio of about 25 to 1. The recoil force caused by the contact of theupper surface 169 of the recoil mass 'or the compressed preload mediumagainst the fixed surface 171 of cap 101 is transmitted through the Cframe 65. This, of course, causes a temporary misalignment of upperhammer unit 79 as well as lower hammer unit 80 from rivet axis 83.However, due to the time lag between the time that coil 163 starts itsrecoil motion and the time that the recoil force is applied to frame 65,heading die 151 has completed its travel and consequent installation ofrivet 87. Thus, the temporary misalignment in the frame 65 has no affectin the accuracy of the setting of the rivet 87.

In one installation similar to riveter 60, the capacitor bank has acapacitance of 360 ufd with a voltage range between 0 to 10,000 volts.With this riveter, the order of magnitude of the impacting force betweenthe rivet forming die surface and the rivet varies up to a static orslow rate equivalent of over 72,000 pounds. The duration of thedie-rivet impact is measured in the range between and 700 microseconds.This duration can be varied by altering electrical and mechanicalconstants of the system to something beyond this range.

Using a riveter installation similar to that shown in FIGS. 2 to 4 inone series of tests, three-sixteenths inch nominal diameter 6AL-4Vtitanium rivets were installed with their deformation equivalent tosqueeze installations requiring 58 to 70 foot-pounds of energy. In thisinstallation the coils had 27 turns each and the peak capacitor bankenergy discharge was between 3,500 to 3,800 Joules at between 4,400 to4,600 volts to produce a peak force of 16,000 to 20,000 pounds. It istherefore seen that the riveter of this invention provides a very highdensity energy impact on the rivet.

In another series of tests utilizing an electromagnetic riveter similarto that shown in FIGS. 2 to 4, it was found that two specimen structureswould not fail after 2,000,000 and 1,750,000 cycles at 60,000 psistress, respectively, so that tests were stopped. Such results areconsidered outstanding when compared to the results of the previousstandard squeeze riveting technique for similar structures which wouldbe considered acceptable if no failure occurred after 300,000 cyclesunder the same test conditions. After sectioning these nonfailing rivetinstallations it was noted that the shank expansion for the cylindricalportion of the rivets, which excludes the countersink portions, weresurprisingly uniform along their length.

For a better understanding of the just mentioned test results, referenceis directed to FIGS. 5 and 6. As shown in FIG. 5 the two sheets ofmaterial to be joined, 85 and 86, are aligned and clamped between theclamping pads 105 and 106. A preload on rivet 87 is provided byengagement between the heading die surfaces 151 and 191 of the riveter60. FIG. 5 shows the relative position of the elements just prior to thedischarge of electrical current through the riveter coils.

In FIG. 6 the condition of the same rivet 87 as it is installed in theplates 85, 86 is shown. The countersink portion 193 has been filled inby the rivet and the shaft of the rivet has become uniformly radiallyexpanded to snugly and firmly fasten the sheets 85, 86 together. Toappreciate the uniformity of shank expansion resulting from the use ofthe improved riveter of the instant invention, the cylindrical expansionof the shank between the boundaries 195 shown in the drawing have'beenmeasured to indicate that in this portion of the rivet there is avariation of less than one percent of the nominal diameter of the rivetbetween the most expanded portion of the rivet and the least expandedportion. Specifically for a rivet having a nominal diameter of 0.250inches a measurement was taken between points 197 and 197, afterinstallation, yielding a measurement of 0.273 inches. A secondmeasurement between points 198 and 198 at the-interface between sheets85 and 86 produced a measurement of 0.271 inches. A third measurementbetween points 199 and 199, at the other end of the cylindrical portionof the rivet, produced a measurement of 0.273 inches. The maximumvariation (0.2730271) is 0.002 inches. One percent of the nominaldiameter would have been 0.0025 inches. The average rivet radialexpansion in a series of tests indicated a range between 3 to 10 percentof the rivets nominal diameter all producing fueltight joints havingextremely good fatigue life. For example, with a nominal rivet diameterof 0.250 an installed average diameter of 0.275 would be considered a 10percent radial expansion. The measurements for uniformity of the rivetshank portion were taken with the distance between the surface of theplate 86 and the point 199 being approximately 10 percent of the shankheight and the distance between the point 197 and the beginning of therivet countersink portion 193 also being equal to about 10 percent ofthe shank height. Thus the span 195 is equal to approximately 80 percentof the shank cylindrical portion. Measurements closer to the countersinkchange or the surface of the sheet 86 are not considered reliable forthe purposes of evaluating the uniformity of shank expansion.

We claim:

1. An apparatus for applying a mechanical force against a workpiececomprising:

first means for generating a first high intensity time varying magneticfield, said first generating means including a first coil having aplurality of turns;

first transducer means, including means defining a first electricallyconductive surface positioned within said first field and means defininga first working surface, for converting the first repulsion forcedeveloped between said conductive surface and said generating means intoa first mechanical force applied to said workpiece by said first workingsurface;

housing means including guiding surfaces for permitting said coil andtransducer means to be slidably supported therealong; and

recoil mass means positioned in force transmitting relationship with theface of said coil remote from said transducer means, and includingsurfaces in sliding contact with said guiding surfaces;

said recoil mass means and said transducer means having a weight ratiogreater than 10 to l.

. 2. The apparatus of claim 1 wherein:

said recoil mass means and said transducer means have a weight ratio of25 to l.

3. The apparatus of claim 1 wherein:

said housing includes means for supporting a workpiece in line with thepath of movement of said working surface.

4. The apparatus of claim 1 wherein:

said housing also includes means for arresting the movement of saidrecoil mass means as it moves away from said transducer.

5. The apparatus of claim 4 wherein:

said housing extends a recoil distance between said workpiece supportingmeans and the other end of said housing sufficient to permit saidworking surface to complete its travel in a first direction toward saidworkpiece before said recoil mass completes its travel in the oppositedirection.

6. An apparatus for applying a mechanical force against a workpiececomprising: 7

first means for generating a first high intensity time varying magneticfield;

first transducer means, including means defining a first electricallyconductive surface positioned within said first field and means defininga first working surface, for converting the first repulsion forcedeveloped between said conductive surface and said generating means intoa first mechanical force applied to said workpiece by said first workingsurface;

second means for generating a second high intensity time varyingmagnetic field;

second transducer means, including means defining a second electricallyconductive surface positioned within said second field and meansdefining a second working surface, for converting the second repulsionforce developed between said second conductive surface and said secondgenerating means into a second mechanical force applied to saidworkpiece by said second working surface in a direction generallyopposite to the direction of said first mentioned mechanical forceapplied to said workpiece;

frame means including first and second support means;

said first support means including first positioning means forpositioning said first field generating means and said first transducermeans providing a first path for movement of said first working surfacein a first direction;

said second support means including second positioning means forpositioning said second field generating means and said secondtransducer means providing a second path for movement of said secondworking surface in a second direction opposite to said first direction;

said first positioning means including first workpiece pad means andfirst clamping motor means operatively connected between said firstsupport means and said first pad means for moving said pad meansrelative to said workpiece along said first and second directions;

said second positioning means including second workpiece padmeans andsecond clamping motor means operatively connected between said secondsupport means and said second pad means for moving said pad meansrelative to said workpiece along said first and second directions andfor applying clamping pressure on opposite sides of said workpiecebetween said first and second pad means.

7. The apparatus of claim 6 including:

said first positioning means also including a first housing means havingfirst guiding surfaces extending in said first and second directions;

said first field generating means including first electric coil meanshaving an axis and external side walls generally parallel to said firstguiding surfaces for guiding said first coil means therealong withinsaid housing;

first recoil mass means positioned in force translating contact with therecoil surface of said first coil;

said first transducer means including side walls formed to slide alongsaid first guiding surfaces with said first conductive surfacepositioned adjacent to the transducer surface of said coil opposite tosaid recoil surface.

8. The apparatus of claim 7 including:

said second positioning means also including a second housing meanshaving second guiding surfaces extending along said first and seconddirections;

said second field generating means including second electric coil meanshaving a second coil axis coincident with said first coil axis andexternal side walls generally parallel to said second guiding surfacesfor guiding said first coil means therealong within said second housing;

second recoil mass means positioned in force translating contact withthe recoil surface of said second coil;

said second transducer means including side walls formed to slide alongsaid guiding surfaces with said second conductive surface positionedadjacent to the transducer surface of said second coil opposite to saidrecoil surface.

9. The apparatus of claim 7 wherein:

said recoil mass including another surface opposite to said surfacecontacting said coil;

said first housing including cap means closing off one end thereof anddefining with said other surface of said recoil mass and said firstguiding surfaces a preload chamber;

said preload chamber adapted to receive a pressure medium therein forurging said first recoil mass, said first coil means, and said firsttransducer in said first direction.

10. The apparatus of claim 1 including: means for cooling said magneticfield generating means.

11. The apparatus of claim 10 wherein:

said cooling means includes means for directing a cooling medium againstand between said magnetic field generating means and said electricallyconductive surface.

12. The apparatus of claim 1 wherein:

said first field generating means includes an electrical energy storagemeans in the form of a capacitor bank having a voltage capacity in therange between 0 to 10,000 volts. 4

13. An electromagnetic power tool apparatus for applying a highintensity impulse of mechanical work force to a workpiece externalthereto comprising:

means for generating a rapidly rising magnetic field of high intensity,said generating means including a flat-wound electrically conductivecoil having a plurality of turns and further including means for passinga high energy impulse of electrical current through said coil; and

transducer means having first and second substantially opposing sidesand including means defining an electrically conductive surface at saidfirst side, said surface being positioned immediately adjacent to a faceof said coil and being electrically isolated from any source of appliedelectrical current, said transducer means further including a forceapplication tool at said second side, said force application tool beingpropelled through a working stroke by the repulsion force developedbetween said conductive surface and said coil upon passing of saidimpulse of electrical current through said coil to thereby generate saidmagnetic field and induce eddy currents in said conductive surface, saidforce application tool being so exposed on said apparatus as to beworkingly engageable at the beginning of said working stroke with aworkpiece external to said apparatus.

14. The apparatus of claim 13 wherein:

said coil is formed of a ribbon of electrically conductive materialhaving a width-to-thickness ratio greater than 1 to 1, said widthextending in a first direction generally parallel to the axis of saidcoil.

15. An apparatus for applying a mechanical force against a workpiececomprising:

first means for generating a first high intensity time varying magneticfield, said first generating means including a first fiat-woundelectrically conductive coil having a plurality of turns;

first transducer means, including means defining a first electricallyconductive surface positioned within said first field and means defininga first working surface, for converting the first repulsion forcedeveloped between said conductive surface and said coil into a firstmechanical force applied to said workpiece by said first workingsurface;

housing means including guiding surfaces for permitting said coil andtransducer means to be slidably supported therealong; and

recoil mass means positioned in force transmitting relationship with theface of said coil remote from said transducer means, and includingsurfaces in sliding contact with said guiding surfaces;

said recoil mass means and said transducer means having a weight ratiogreater than 10 to l.

16. The apparatus of claim 15 wherein:

said recoil mass means and said transducer means have a weight ratio of25 to 1.

17. The apparatus of claim 15 wherein:

said housing extends a recoil distance between said a workpiecesupporting means and the other end of said housing sufficient to permitsaid working surface to complete its travel in a first direction towardsaid workpiece before said recoil mass completes its travel in theopposite direction.

20. An apparatus for applying amechanical force against a workpiececomprising:

first means for generating a first high intensity time varying magneticfield, said first generating means including a first flat-woundelectrically conductive coil having a plurality of turns;

first transducer means, including means defining a first electricallyconductive surface positioned within said first field and means defininga first working surface, for converting the first repulsion forcedeveloped between said conductive surface and said coil into a firstmechanical force applied to said workpiece by said first workingsurface;

second means for generating a second high intensity time varyingmagnetic field, said second generating means including a secondflat-wound electrically conductive coil having a plurality of turns; and

second transducer means, including means defining a second electricallyconductive surface positioned within said second field and meansdefining a second working surface, for converting the second repulsionforce developed between said second conductive surface and said secondcoil into a second mechanical force applied to said workpiece by saidsecond working surface in a direction generally opposite to thedirection of said first mentioned mechanical force applied to saidworkpiece.

21. The apparatus of claim wherein:

said first and second generating means include means for electricallyconnecting said first and second coils in series for simultaneouslygenerating said first and second magnetic fields.

22. The apparatus of claim 20 including:

frame means including first and second support means;

said first support means including first positioning means forpositioning said first coil and said first transducer means providing afirst path for movement of said first working surface in a firstdirection;

said second support means including second positioning means forpositioning said second coil and said second transducer means providinga second path for movement of said second working surface in a seconddirection opposite to said first direction.

23. The apparatus of claim 22 wherein:

said first positioning means including first workpiece pad means andfirst clamping motor means operatively connected between said firstsupport means and said first pad means for moving said pad meansrelative to said workpiece along said first and second directions;

said second positioning means including ,second workpiece pad means andsecond clamping motor means operatively connected between said secondsupport means and said second pad 'means for moving said pad meansrelative to said workpiece along said first and second directions andfor applying clamping pressure on opposite sides of said workpiecebetween said first and second pad means.

24. The apparatus of claim 23 including:

first recoil mass means positioned in force translating contact with therecoil surface of said first coil;

said first positioning means also including a first housing means havingfirst guiding surfaces extending in said first and second directions;

said first coil having external side walls generally parallel to saidfirst guiding surfaces for guiding said first coil means therealongwithin said houss;

said first transducer means including side walls formed to slide alongsaid first guiding surfaces with said first conductive surfacepositioned adjacent to the transducer surface of said first coilopposite to said recoil surface.

25. The apparatus of claim 24 including:

second recoil mass means positioned in force translating contact withthe recoil surface of said second coil;

said second positioning means also including a second housing meanshaving second guiding surfaces extending along said first and seconddirections;

said second coil having a second coil axis coincident with said firstcoil axis and external side walls generally parallel to said secondguiding surfaces for guiding said first coil means therealong withinsaid second housing;

said second transducermeans including side walls formed to slide alongsaid second guiding surfaces with said second conductive surfacepositioned adjacent to the transducer surface of said second coilopposite to said recoil surface.

26. The apparatus of claim 24 wherein:

said first recoil mass including another surface opposite to saidsurface contracting said first coil;

said first housing including cap means closing off one end thereof anddefining with said other surface of said first rec oil mass and saidfirst guiding surfaces a preload chamber;

said preload chamber adapted to receive a pressure medium therein forurging said first recoil mass, said first coil means, and said firsttransducer in said first direction.

27. The apparatus of claim 13 wherein:

said first field generating means includes an electrical energy storagemeans in the form of a capacitor bank.

28. The apparatus of claim 27 wherein:

said capacitor bank has a voltage capacity in the range between 0 to10,000 volts.

29. The apparatus of claim 13 wherein said force application tool is arivet heading die.

1. An apparatus for applying a mechanical force against a workpiececomprising: first means for generating a first high intensity timevarying magnetic field, said first generating means including a firstcoil having a plurality of turns; first transducer means, includingmeans defining a first electrically conductive surface positioned withinsaid first field and means defining a first working surface, forconverting the first repulsion force developed between said conductivesurface and said generating means into a first mechanical force appliedto said workpiece by said first working surface; housing means includingguiding surfaces for permitting said coil and transducer means to beslidably supported therealong; and recoil mass means positioned in forcetransmitting relationship with the face of said coil remote from saidtransducer means, and including surfaces in sliding contact with saidguiding surfaces; said recoil mass means and said transducer meanshaving a weight ratio greater than 10 to
 1. 2. The apparatus of claim 1wherein: said recoil mass means and said transducer means have a weightratio of 25 to
 1. 3. The apparatus of claim 1 wherein: said housingincludes means for supporting a workpiece in line with the path ofmovement of said working surface.
 4. The apparatus of claim 1 wherein:said housing also includes means for arresting the movement of saidrecoil mass means as it moves away from said transducer.
 5. Theapparatus of claim 4 wherein: said housing extends a recoil distancebetween said workpiece supporting means and the other end of saidhousing sufficient to permit said working surface to complete its travelin a first directioN toward said workpiece before said recoil masscompletes its travel in the opposite direction.
 6. An apparatus forapplying a mechanical force against a workpiece comprising: first meansfor generating a first high intensity time varying magnetic field; firsttransducer means, including means defining a first electricallyconductive surface positioned within said first field and means defininga first working surface, for converting the first repulsion forcedeveloped between said conductive surface and said generating means intoa first mechanical force applied to said workpiece by said first workingsurface; second means for generating a second high intensity timevarying magnetic field; second transducer means, including meansdefining a second electrically conductive surface positioned within saidsecond field and means defining a second working surface, for convertingthe second repulsion force developed between said second conductivesurface and said second generating means into a second mechanical forceapplied to said workpiece by said second working surface in a directiongenerally opposite to the direction of said first mentioned mechanicalforce applied to said workpiece; frame means including first and secondsupport means; said first support means including first positioningmeans for positioning said first field generating means and said firsttransducer means providing a first path for movement of said firstworking surface in a first direction; said second support meansincluding second positioning means for positioning said second fieldgenerating means and said second transducer means providing a secondpath for movement of said second working surface in a second directionopposite to said first direction; said first positioning means includingfirst workpiece pad means and first clamping motor means operativelyconnected between said first support means and said first pad means formoving said pad means relative to said workpiece along said first andsecond directions; said second positioning means including secondworkpiece pad means and second clamping motor means operativelyconnected between said second support means and said second pad meansfor moving said pad means relative to said workpiece along said firstand second directions and for applying clamping pressure on oppositesides of said workpiece between said first and second pad means.
 7. Theapparatus of claim 6 including: said first positioning means alsoincluding a first housing means having first guiding surfaces extendingin said first and second directions; said first field generating meansincluding first electric coil means having an axis and external sidewalls generally parallel to said first guiding surfaces for guiding saidfirst coil means therealong within said housing; first recoil mass meanspositioned in force translating contact with the recoil surface of saidfirst coil; said first transducer means including side walls formed toslide along said first guiding surfaces with said first conductivesurface positioned adjacent to the transducer surface of said coilopposite to said recoil surface.
 8. The apparatus of claim 7 including:said second positioning means also including a second housing meanshaving second guiding surfaces extending along said first and seconddirections; said second field generating means including second electriccoil means having a second coil axis coincident with said first coilaxis and external side walls generally parallel to said second guidingsurfaces for guiding said first coil means therealong within said secondhousing; second recoil mass means positioned in force translatingcontact with the recoil surface of said second coil; said secondtransducer means including side walls formed to slide along said guidingsurfaces with said second conductive surface positioned adjacent to thetransducer surface of said second coil opposite to said recoil surfAce.9. The apparatus of claim 7 wherein: said recoil mass including anothersurface opposite to said surface contacting said coil; said firsthousing including cap means closing off one end thereof and definingwith said other surface of said recoil mass and said first guidingsurfaces a preload chamber; said preload chamber adapted to receive apressure medium therein for urging said first recoil mass, said firstcoil means, and said first transducer in said first direction.
 10. Theapparatus of claim 1 including: means for cooling said magnetic fieldgenerating means.
 11. The apparatus of claim 10 wherein: said coolingmeans includes means for directing a cooling medium against and betweensaid magnetic field generating means and said electrically conductivesurface.
 12. The apparatus of claim 1 wherein: said first fieldgenerating means includes an electrical energy storage means in the formof a capacitor bank having a voltage capacity in the range between 0 to10,000 volts.
 13. An electromagnetic power tool apparatus for applying ahigh intensity impulse of mechanical work force to a workpiece externalthereto comprising: means for generating a rapidly rising magnetic fieldof high intensity, said generating means including a flat-woundelectrically conductive coil having a plurality of turns and furtherincluding means for passing a high energy impulse of electrical currentthrough said coil; and transducer means having first and secondsubstantially opposing sides and including means defining anelectrically conductive surface at said first side, said surface beingpositioned immediately adjacent to a face of said coil and beingelectrically isolated from any source of applied electrical current,said transducer means further including a force application tool at saidsecond side, said force application tool being propelled through aworking stroke by the repulsion force developed between said conductivesurface and said coil upon passing of said impulse of electrical currentthrough said coil to thereby generate said magnetic field and induceeddy currents in said conductive surface, said force application toolbeing so exposed on said apparatus as to be workingly engageable at thebeginning of said working stroke with a workpiece external to saidapparatus.
 14. The apparatus of claim 13 wherein: said coil is formed ofa ribbon of electrically conductive material having a width-to-thicknessratio greater than 1 to 1, said width extending in a first directiongenerally parallel to the axis of said coil.
 15. An apparatus forapplying a mechanical force against a workpiece comprising: first meansfor generating a first high intensity time varying magnetic field, saidfirst generating means including a first flat-wound electricallyconductive coil having a plurality of turns; first transducer means,including means defining a first electrically conductive surfacepositioned within said first field and means defining a first workingsurface, for converting the first repulsion force developed between saidconductive surface and said coil into a first mechanical force appliedto said workpiece by said first working surface; housing means includingguiding surfaces for permitting said coil and transducer means to beslidably supported therealong; and recoil mass means positioned in forcetransmitting relationship with the face of said coil remote from saidtransducer means, and including surfaces in sliding contact with saidguiding surfaces; said recoil mass means and said transducer meanshaving a weight ratio greater than 10 to
 1. 16. The apparatus of claim15 wherein: said recoil mass means and said transducer means have aweight ratio of 25 to
 1. 17. The apparatus of claim 15 wherein: saidhousing includes means for supporting a workpiece in line with the pathof movement of said working surface.
 18. The apparatus of Claim 15wherein: said housing also includes means for arresting the movement ofsaid recoil mass means as it moves away from said transducer.
 19. Theapparatus of claim 18 wherein: said housing extends a recoil distancebetween said workpiece supporting means and the other end of saidhousing sufficient to permit said working surface to complete its travelin a first direction toward said workpiece before said recoil masscompletes its travel in the opposite direction.
 20. An apparatus forapplying a mechanical force against a workpiece comprising: first meansfor generating a first high intensity time varying magnetic field, saidfirst generating means including a first flat-wound electricallyconductive coil having a plurality of turns; first transducer means,including means defining a first electrically conductive surfacepositioned within said first field and means defining a first workingsurface, for converting the first repulsion force developed between saidconductive surface and said coil into a first mechanical force appliedto said workpiece by said first working surface; second means forgenerating a second high intensity time varying magnetic field, saidsecond generating means including a second flat-wound electricallyconductive coil having a plurality of turns; and second transducermeans, including means defining a second electrically conductive surfacepositioned within said second field and means defining a second workingsurface, for converting the second repulsion force developed betweensaid second conductive surface and said second coil into a secondmechanical force applied to said workpiece by said second workingsurface in a direction generally opposite to the direction of said firstmentioned mechanical force applied to said workpiece.
 21. The apparatusof claim 20 wherein: said first and second generating means includemeans for electrically connecting said first and second coils in seriesfor simultaneously generating said first and second magnetic fields. 22.The apparatus of claim 20 including: frame means including first andsecond support means; said first support means including firstpositioning means for positioning said first coil and said firsttransducer means providing a first path for movement of said firstworking surface in a first direction; said second support meansincluding second positioning means for positioning said second coil andsaid second transducer means providing a second path for movement ofsaid second working surface in a second direction opposite to said firstdirection.
 23. The apparatus of claim 22 wherein: said first positioningmeans including first workpiece pad means and first clamping motor meansoperatively connected between said first support means and said firstpad means for moving said pad means relative to said workpiece alongsaid first and second directions; said second positioning meansincluding second workpiece pad means and second clamping motor meansoperatively connected between said second support means and said secondpad means for moving said pad means relative to said workpiece alongsaid first and second directions and for applying clamping pressure onopposite sides of said workpiece between said first and second padmeans.
 24. The apparatus of claim 23 including: first recoil mass meanspositioned in force translating contact with the recoil surface of saidfirst coil; said first positioning means also including a first housingmeans having first guiding surfaces extending in said first and seconddirections; said first coil having external side walls generallyparallel to said first guiding surfaces for guiding said first coilmeans therealong within said housing; said first transducer meansincluding side walls formed to slide along said first guiding surfaceswith said first conductive surface positioned adjacent to the transducersurface of said first coil opposite to said recoil surfaCe.
 25. Theapparatus of claim 24 including: second recoil mass means positioned inforce translating contact with the recoil surface of said second coil;said second positioning means also including a second housing meanshaving second guiding surfaces extending along said first and seconddirections; said second coil having a second coil axis coincident withsaid first coil axis and external side walls generally parallel to saidsecond guiding surfaces for guiding said first coil means therealongwithin said second housing; said second transducer means including sidewalls formed to slide along said second guiding surfaces with saidsecond conductive surface positioned adjacent to the transducer surfaceof said second coil opposite to said recoil surface.
 26. The apparatusof claim 24 wherein: said first recoil mass including another surfaceopposite to said surface contracting said first coil; said first housingincluding cap means closing off one end thereof and defining with saidother surface of said first recoil mass and said first guiding surfacesa preload chamber; said preload chamber adapted to receive a pressuremedium therein for urging said first recoil mass, said first coil means,and said first transducer in said first direction.
 27. The apparatus ofclaim 13 wherein: said first field generating means includes anelectrical energy storage means in the form of a capacitor bank.
 28. Theapparatus of claim 27 wherein: said capacitor bank has a voltagecapacity in the range between 0 to 10,000 volts.
 29. The apparatus ofclaim 13 wherein said force application tool is a rivet heading die. 30.The apparatus of claim 13 wherein said electrically conductive surfaceis substantially equal in size and shape to said face of said coil andis positioned symmetrically with respect to said face.
 31. The apparatusof claim 13 wherein said force application tool is a rivet heading die.